A display device may include a light guide that transmits an image to a display surface, focuses an image on a detector, or does both. For some applications, the light guide may be wedge-shaped, transparent in one or more visible, ultraviolet, and/or infrared wavelength ranges, and comprise at least one pair of opposing faces. Light may propagate through the light guide via internal reflection from the opposing faces and emerge from at least one face as a collimated image.
The quality of the image provided by the display device may depend on the roughness of the opposing faces of the light guide, where internal reflection takes place. For some applications, an average roughness of ±2 nanometers or less may be desired for superior image quality. Depending on the application, certain optical features—Fresnel lens features, for example—may also be provided in the light guide. A high degree of smoothness and dimensional fidelity may be desired for these features as well, and may be achieved using specialized optical materials and/or complex etching and polishing procedures. However, light guides made using such materials and procedures may be too expensive for many applications.